Embodiments relate generally to marine geophysical surveying and, more particularly, embodiments relate to calibration of an accelerometer while deployed in the water.
Techniques for geophysical surveying include marine geophysical surveying, such as seismic surveying and electromagnetic surveying, in which geophysical data may be collected from below the Earth's surface. Geophysical surveying has applications in mineral and energy exploration and production to help identify locations of hydrocarbon-bearing formations. Certain types of marine geophysical surveying, such as seismic or electromagnetic surveying, may include towing an energy source at a selected depth—typically above the seafloor—in a body of water. One or more streamers also may be towed in the water at selected depths—typically above the seafloor—by the same or a different vessel. The streamers are typically cables that include a plurality of geophysical sensors disposed thereon at spaced apart locations along the length of the cable. Some geophysical surveys locate sensors on ocean bottom cables or nodes in addition to, or instead of, streamers. The geophysical sensors may be configured to generate a signal that is related to a parameter being measured by the geophysical sensor. At selected times, the energy source may be actuated to generate, for example, seismic or electromagnetic energy that travels downwardly into the subsurface rock. Energy that interacts with interfaces, generally at the boundaries between layers of rock formations, may be returned toward the surface and detected by the geophysical sensors on the streamers. The detected energy may he used to infer certain properties of the subsurface rock, such as structure, mineral composition and fluid content, thereby providing information useful in the recovery of hydrocarbons.
The geophysical sensors employed on the streamers may be vector sensors. Vector sensors may also be deployed on the streamer as rotation sensors to determine streamer location, velocity, or orientation. Examples of suitable vector sensors include those that comprise accelerometers. In some instances, the accelerometers may be multi-axis accelerometers. In some instances, the accelerometers may utilize a microelectromechanical (MEMS) based structure. Accelerometers may typically output a DC-coupled signal proportional to the acceleration applied to the device. However, usage of accelerometers may be problematic as the accelerometers may experience a DC bias and gain drift, which can negatively impact sensor performance. In some accelerometers, axial misalignment may also be a concern. Improved accelerometers that do not exhibit these drawbacks may be cost prohibitive. Thus, there is a need for improved calibration methods able to compensate for the non-idealities of the accelerometers.